Inspection steps are interspersed throughout a semiconductor production process in order to monitor product quality and to identify and isolate problems which negatively impact a production yield. Inspection steps are performed using either electromagnetic detection, in which electromagnetic waves are incident on a device surface and an angle of reflection or refraction of the electromagnetic waves is detected, or electron beam (e-beam) inspection, in which a stream of electrons are incident on the device surface and electrons returned from the surface are detected. E-beam inspection is a more time consuming process than optical detection; however, e-beam inspection has higher resolution capabilities than optical detection.
As the processing node for semiconductor manufacturing decreases, the detection of abnormalities in features formed on a wafer using electromagnetic detection becomes more difficult because a signal-to-noise ratio (SNR) decreases to a point where differentiation between a detected signal and background noise is not precise. As the SNR approaches 1.0, the amount of noise is equal to the detected signal making differentiation between the two impossible.